fix: resolve CI segfaults in contour plotting functions

BACKLOG.md

@@ -4,7 +4,6 @@
 
 
 **🚨 CRITICAL: CI test suite failures - user-visible rendering broken**
-- [ ] #401: Fix - CI test-coverage failing with segfaults in colored_contours and ascii_heatmap_demo (blocks all PR merges)
 
 **🚨 CRITICAL: User-visible PNG/PDF rendering regressions**
 
@@ -13,9 +12,10 @@
 
 **Infrastructure & Documentation Issues (Lower Priority)**
 - [ ] #388: Fix - investigate test_mpeg_consolidated failure unrelated to ylabel rotation (test infrastructure)
+- [ ] #403: Refactor - reduce contour function complexity - functions exceed 50-line target
 
 ## DOING (Current Work)
-*Empty - ready for next issue*
+- [x] #401: Fix - CI test-coverage failing with segfaults in colored_contours and ascii_heatmap_demo (branch: fix-ci-segfaults-401)
 
 ## FUTURE SPRINTS - Systematic Restoration
 

src/fortplot_matplotlib.f90

@@ -108,12 +108,42 @@ subroutine contour_filled(x, y, z, levels, colormap, show_colorbar, label)
             allocate(wp_levels(0))
         end if
 
-        ! Forward ALL parameters to underlying method using single call pattern
-        call fig%add_contour_filled(wp_x, wp_y, wp_z, &
-            levels=merge(wp_levels, wp_levels, present(levels)), &
-            colormap=merge(colormap, "", present(colormap)), &
-            show_colorbar=merge(show_colorbar, .false., present(show_colorbar)), &
-            label=merge(label, "", present(label)))
+        ! Forward parameters to underlying method using conditional calls for memory safety
+        if (present(levels) .and. present(colormap) .and. present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, show_colorbar=show_colorbar, label=label)
+        else if (present(levels) .and. present(colormap) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, show_colorbar=show_colorbar)
+        else if (present(levels) .and. present(colormap) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, label=label)
+        else if (present(colormap) .and. present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, &
+                show_colorbar=show_colorbar, label=label)
+        else if (present(levels) .and. present(colormap)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, colormap=colormap)
+        else if (present(levels) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, show_colorbar=show_colorbar)
+        else if (present(levels) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, label=label)
+        else if (present(colormap) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, show_colorbar=show_colorbar)
+        else if (present(colormap) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, label=label)
+        else if (present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, show_colorbar=show_colorbar, label=label)
+        else if (present(levels)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels)
+        else if (present(colormap)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap)
+        else if (present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, show_colorbar=show_colorbar)
+        else if (present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, label=label)
+        else
+            call fig%add_contour_filled(wp_x, wp_y, wp_z)
+        end if
 
         deallocate(wp_x, wp_y, wp_z)
         if (allocated(wp_levels)) deallocate(wp_levels)
@@ -433,12 +463,42 @@ subroutine add_contour_filled(x, y, z, levels, colormap, show_colorbar, label)
             allocate(wp_levels(0))
         end if
 
-        ! Forward ALL parameters to underlying method using single call pattern
-        call fig%add_contour_filled(wp_x, wp_y, wp_z, &
-            levels=merge(wp_levels, wp_levels, present(levels)), &
-            colormap=merge(colormap, "", present(colormap)), &
-            show_colorbar=merge(show_colorbar, .false., present(show_colorbar)), &
-            label=merge(label, "", present(label)))
+        ! Forward parameters to underlying method using conditional calls for memory safety
+        if (present(levels) .and. present(colormap) .and. present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, show_colorbar=show_colorbar, label=label)
+        else if (present(levels) .and. present(colormap) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, show_colorbar=show_colorbar)
+        else if (present(levels) .and. present(colormap) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, &
+                colormap=colormap, label=label)
+        else if (present(colormap) .and. present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, &
+                show_colorbar=show_colorbar, label=label)
+        else if (present(levels) .and. present(colormap)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, colormap=colormap)
+        else if (present(levels) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, show_colorbar=show_colorbar)
+        else if (present(levels) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels, label=label)
+        else if (present(colormap) .and. present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, show_colorbar=show_colorbar)
+        else if (present(colormap) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap, label=label)
+        else if (present(show_colorbar) .and. present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, show_colorbar=show_colorbar, label=label)
+        else if (present(levels)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, levels=wp_levels)
+        else if (present(colormap)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, colormap=colormap)
+        else if (present(show_colorbar)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, show_colorbar=show_colorbar)
+        else if (present(label)) then
+            call fig%add_contour_filled(wp_x, wp_y, wp_z, label=label)
+        else
+            call fig%add_contour_filled(wp_x, wp_y, wp_z)
+        end if
 
         deallocate(wp_x, wp_y, wp_z)
         if (allocated(wp_levels)) deallocate(wp_levels)

test/test_contour_memory_safety_regression.f90

@@ -0,0 +1,113 @@
+program test_contour_memory_safety_regression
+    !! Test to prevent memory safety regressions in contour plotting
+    !! Specifically tests the segfault issue fixed in Issue #401 related to merge() function
+    use fortplot
+    implicit none
+
+    call test_contour_filled_no_optional_args()
+    call test_contour_filled_with_colormap_only()
+    call test_add_contour_filled_no_optional_args() 
+    call test_add_contour_filled_with_colormap_only()
+
+    print *, "All contour memory safety regression tests passed!"
+
+contains
+
+    subroutine test_contour_filled_no_optional_args()
+        !! Test contour_filled with no optional arguments - this caused segfault in Issue #401
+        real(wp), dimension(10) :: x_grid, y_grid
+        real(wp), dimension(10,10) :: z_grid
+        integer :: i, j
+
+        ! Generate simple test data
+        do i = 1, 10
+            x_grid(i) = (i-1) * 0.5_wp
+            y_grid(i) = (i-1) * 0.5_wp
+        end do
+
+        do i = 1, 10
+            do j = 1, 10
+                z_grid(i,j) = sin(x_grid(i)) * cos(y_grid(j))
+            end do
+        end do
+
+        ! This should NOT segfault - the merge() issue was here
+        call figure()
+        call contour_filled(x_grid, y_grid, z_grid)  
+
+        print *, "✓ contour_filled with no optional args - PASSED"
+    end subroutine test_contour_filled_no_optional_args
+
+    subroutine test_contour_filled_with_colormap_only()
+        !! Test contour_filled with only colormap argument
+        real(wp), dimension(5) :: x_grid, y_grid
+        real(wp), dimension(5,5) :: z_grid
+        integer :: i, j
+
+        ! Generate simple test data
+        do i = 1, 5
+            x_grid(i) = (i-1) * 1.0_wp
+            y_grid(i) = (i-1) * 1.0_wp
+        end do
+
+        do i = 1, 5
+            do j = 1, 5
+                z_grid(i,j) = x_grid(i) + y_grid(j)
+            end do
+        end do
+
+        call figure()
+        call contour_filled(x_grid, y_grid, z_grid, colormap="plasma")
+
+        print *, "✓ contour_filled with colormap only - PASSED"
+    end subroutine test_contour_filled_with_colormap_only
+
+    subroutine test_add_contour_filled_no_optional_args()
+        !! Test add_contour_filled with no optional arguments 
+        real(wp), dimension(8) :: x_grid, y_grid
+        real(wp), dimension(8,8) :: z_grid
+        integer :: i, j
+
+        ! Generate simple test data
+        do i = 1, 8
+            x_grid(i) = (i-1) * 0.25_wp
+            y_grid(i) = (i-1) * 0.25_wp
+        end do
+
+        do i = 1, 8
+            do j = 1, 8
+                z_grid(i,j) = exp(-(x_grid(i)**2 + y_grid(j)**2))
+            end do
+        end do
+
+        call figure()
+        call add_contour_filled(x_grid, y_grid, z_grid)  
+
+        print *, "✓ add_contour_filled with no optional args - PASSED"
+    end subroutine test_add_contour_filled_no_optional_args
+
+    subroutine test_add_contour_filled_with_colormap_only()
+        !! Test add_contour_filled with only colormap argument
+        real(wp), dimension(6) :: x_grid, y_grid
+        real(wp), dimension(6,6) :: z_grid
+        integer :: i, j
+
+        ! Generate simple test data
+        do i = 1, 6
+            x_grid(i) = (i-1) * 0.4_wp
+            y_grid(i) = (i-1) * 0.4_wp
+        end do
+
+        do i = 1, 6
+            do j = 1, 6
+                z_grid(i,j) = x_grid(i)**2 - y_grid(j)**2
+            end do
+        end do
+
+        call figure()
+        call add_contour_filled(x_grid, y_grid, z_grid, colormap="inferno")
+
+        print *, "✓ add_contour_filled with colormap only - PASSED"
+    end subroutine test_add_contour_filled_with_colormap_only
+
+end program test_contour_memory_safety_regression